The Night Sky April 2010
Compiled by Ian Morison
This page, updated monthly, will let you know some of the things that you can look out for in the night sky. It lists the phases of the Moon, where you will see the naked-eye planets and describes some of the prominent constellations in the night sky during the month.
Image of the Month
The Hickson 31 galaxy group Image:NASA/ESA
In this image of the Hickson compact group 31, several of the dwarf galaxies are in the slow process of merging - perhaps to form a giant elliptical galaxy. Two galaxies on the lower left are in the process of merging and an elongated galaxy above is connected to them by a bridge of stars. There is also a trail of stars between them and the spiral galaxy to the lower right of the image. The final merged galaxy is likely to appear about 1 billion years from now. The group lies about 150 million light years distant in the constellation Eridani and spans about 150,000 light years - about 50% greater than the size of our own Milky Way galaxy.
Highlights of the Month
First Week April: Venus and Mercury together after Sunset.
First week of April: Venus and Mercury close in the twilight sky
Given a low westerly horizon and a clear night you will have a chance to see Venus and Mercury just a few degrees apart about 30 minutes after sunset. Until April 7th both are moving away from the Sun so getting higher in the sky after sunset. From the 8th April, Mercury begins to move back toward the Sun and by the 21st of the month will be very difficult to spot in glare of the sunset. Their closest approach, at 3 degrees separation, will be on April 4th. This is the best evening apparition of Mercury this year and occurs as, at this time of the year, the ecliptic is well inclined to the evening horizon. On the 15th April, Mercury is just below a very thin (one day old) crescent Moon. You will need a very clear low western horizon to have a chance of spotting this!
16-18th April: Mars and the Beehive Cluster.
16-18th April: Mars passes the Beehive Cluster
Having resumed its easterly path through Cancer, Mars passes close to M44, the Beehive Cluster, around the 17th April. This should be a nice sight with binoculars. As Mars moves away to the upper left of M44, they are joined by the first quarter Moon on the 21st April.
The Lyrid meteor Shower on the night of 22/23rd April
The Lyrid Meteor Shower - so called as the radiant (from where the meteor trails seem to radiate from) lies in the constellation Lyra. It peaks in the early morning of the 22nd April and is a reliable, though not spectacular, shower with perhaps up to 15 meteors seen per hour. Observations of the Lyrid meteors have been made for at least 2,600 years! This year the peak of activity is close to the first quarter moon which, happily, will have set before the best time to observe the shower. Observations made after 1 am are expected to be the most productive. The dust particles that cause the shower have been released by the comet Thatcher, discovered in 1861. Occasionally we pass through a dense clump of particles as happened in 1982 when over 90 meteors were seen per hour. So its worth waking up to have a look if clear around 1-2 am. Look to the East as shown in the chart.
Observe the International Space Station
The International Space Station and Jules Verne passing behind the Lovell Telescope on April 1st 2008.
Image by Andrew Greenwood
Use the link below to find when the space station will be visible in the next few days. In general, the space station can be seen either in the hour or so before dawn or the hour or so after sunset - this is because it is dark and yet the Sun is not too far below the horizon so that it can light up the space station. As the orbit only just gets up the the latitude of the UK it will usually be seen to the south, and is only visible for a minute or so at each sighting. Note that as it is in low-earth orbit the sighting details vary quite considerably across the UK. The NASA website linked to below gives details for several cities in the UK. (Across the world too for foreign visitors to this web page.)
Note: I observed the ISS three times recently and was amazed as to how bright it has become.
Find details of sighting possibilities from your location from: Location Index
See where the space station is now: Current Position
The Moon at 3rd Quarter. Image, by Ian Morison, taken with a 150mm Maksutov-Newtonian and Canon G7.
Just below the crator Plato seen near the top of the image is the mountain "Mons Piton". It casts a long shadow across the maria from which one can calculate its height - about 6800ft or 2250m.
|new moon||first quarter||full moon||last quarter|
|April 14th||April 21st||April 28th||April 6th|
Some Lunar Images by Ian Morison, Jodrell Bank Observatory: Lunar Images
A World Record Lunar Image
To mark International Year of Astronomy, a team of british astronomers have made the largest lunar image in history and gained a place in the Guinness Book of Records! The whole image comprises 87.4 megapixels with a Moon diameter of 9550 pixels. This allows details as small as 1km across to be discerned! The superb quality of the image is shown by the detail below of Plato and the Alpine Valley. Craterlets are seen on the floor of Plato and the rille along the centre of the Alpine valley is clearly visible. The image quality is staggering! The team of Damian Peach, Pete lawrence, Dave Tyler, Bruce Kingsley, Nick Smith, Nick Howes, Trevor Little, David Mason, Mark and Lee Irvine with technical support from Ninian Boyle captured the video sequences from which 288 individual mozaic panes were produced. These were then stitched together to form the lunar image.
Please follow the link to the Lunar World Record website and it would be really great if you could donate to Sir Patrick Moore's chosen charity to either download a full resolution image or purchase a print.
Jupiter, having passed behind the Sun on the 28th February, has now reappeared in the pre-dawn sky. On the first day of April it will rise about 50 minutes before the Sun and, at magnitude -2, could be seen in binoculars given a clear low eastern horizon. During the month it will gradually rise earlier and, by end of the month, will rise about 2 hours earlier than the Sun. Best wait a month or so to see it well though!
Saturn was at opposition on March 21st/22nd so is now easily seen in the south-east after sunset lying to the lower left of the constellation Leo. It can thus be seen for much of the night with a magnitude +0.6 rising to +0,8 during the month. The angular size of the disc stays around 19 arc seconds with the rings extending to 43 arc seconds. The ring system is still close to edge on and so will still appear very thin - the reason why Saturn is not a bright as it is when the rings are more open. Due to difference between the orbital inclinations of Saturn and the Earth, the tilt is actually reducing at the moment, starting the month at an angle of ~3 degrees. This will reduce to only 1.7 degrees in late May before the rings finally begin to open out again from the end of June onwards. For the first time in 15 years we are now begining to see the northern face of the rings. A small telescope will easily show its brightest satellite, Titan at magnitude 7.8, and one of 8 inches or more aperture several more.
Mercury appeared in the twilight sky along with Venus during the last week of March and, in the first two weeks of April, can be spotted with binoculars about 30 minutes after sunset just to the upper left of where the Sun has set. See highlight above.
Mars remains prominent (at magnitude +0.2 falling to +0.7 during the month) high in the south after sunset. Now in Cancer, it has resumed eastwards track across the skies towards Leo. Its angular size angular size drops from 9 to 7 arc seconds during the month so details on the surface will be very hard to spot. See highlight above.
Venus is now prominent in the evening sky after sunset as it climbs ever higher during the month. At magnitude -3.9, it will be easily spotted - the brightest object in the night sky after the Moon. Look towards the south west about half an hour after sunset. With an angular size of ~11 arc seconds it will appear in a telescope as a well illuminated disc like that in the accompanying image. It was this observation by Galileo that showed that Venus must orbit the Sun - should it, as in the Ptolomaic system, be moving in an epicycle between the Sun and the Earth, it could never show a fully illuminated disk! It is an interesting fact that Venus's brightness remains pretty constant at ~ -3.8 to -4 all the time that it is visible. As it nears the Earth, it become a thin crescent, but the fact that it is then much nearer to us means that the effective reflecting area remains virtually constant in apparent size.See highlight above.
Find more planetary images and details about the Solar System: The Solar System
The mid evening April Sky
This map shows the constellations seen in the south in mid-evening.
The constellation Gemini is now setting towards the south-west and Leo holds pride (sic) of place in the south with its bright star Regulus. Between Gemini and Leo lies Cancer. Close to the boundary of these two constellation is where, this month, the planet Saturn may be found. It is well worth observing with binoculars to see the Beehive Cluster at its heart. Below Gemini is the tiny constellation of Canis Minor whose only bright star is Procyon. Rising in the south-east is the constellation Virgo whose brightest star is Spica. Though Virgo has few bright stars it is in the direction of of a great cluster of galaxies - the Virgo Cluster - which lies at the centre of the supercluster of which our local group of galaxies is an outlying member. The constellation Ursa Major is high in the northern sky during the evening this month and contains many interesting objects.
The constellation Gemini
Gemini - The Twins - lies up and to the left of Orion and is in the south-west during early evenings this month. It contains two bright stars Castor and Pollux of 1.9 and 1.1 magnitudes respectivly. Castor is a close double having a separation of ~ 3.6 arc seconds making it a fine test of the quality of a small telescope - providing the atmospheric seeing is good! In fact the Castor system has 6 stars - each of the two seen in the telescope is a double star, and there is a third, 9th magnitude, companion star 73 arcseconds away which is alos a double star! Pollux is a red giant star of spectral class K0. The planet Pluto was discovered close to delta Geminorum by Clyde Tombaugh in 1930. The variable star shown to the lower right of delta Geminorum is a Cepheid variable, changing its brightness from 3.6 to 4.2 magnitudes with a period of 10.15 days
M35 and NGC 2158
This wonderful image was taken by Fritz Benedict and David Chappell using a 30" telescope at McDonal Observatory. Randy Whited combined the three colour CCD images to make the picture
M35 is an open star cluster comprising several hundred stars around a hundred of which are brighter than magnitude 13 and so will be seen under dark skies with a relativly small telescope. It is easily spotted with binoculars close to the "foot" of the upper right twin. A small telescope at low power using a wide field eyepiece will show it at its best. Those using larger telescopes - say 8 to 10 inches - will spot a smaller compact cluster NGC 2158 close by. NGC 2158 is four times more distant that M35 and ten times older, so the hotter blue stars will have reached the end of their lives leaving only the longer-lived yellow stars like our Sun to dominate its light.
To the lower right of the constellation lies the Planetary Nebula NGC2392. As the Hubble Space Telescope image shows, it resembles a head surrounded by the fur collar of a parka hood - hence its other name The Eskimo Nebula. The white dwarf remnant is seen at the centre of the "head". The Nebula was discovered by William Herschel in 1787. It lies about 5000 light years away from us.
The constellation Leo
The constellation Leo is now in the south-eastern sky in the evening. One of the few constellations that genuinely resembles its name, it looks likes one of the Lions in Trafalger Square, with its main and head forming an arc (called the Sickle) to the upper right, with Regulus in the position of its right knee. Regulus is a blue-white star, five times bigger than the sun at a distance of 90 light years. It shines at magnitude 1.4. Algieba, which forms the base of the neck, is the second brightest star in Leo at magnitude 1.9. With a telescope it resolves into one of the most magnificent double stars in the sky - a pair of golden yellow stars! They orbit their common centre of gravity every 600 years. This lovely pair of orange giants are 170 light years away.
Leo also hosts two pairs of Messier galaxies which lie beneath its belly. The first pair lie about 9 degrees to the west of Regulus and comprise M95 (to the east) and M96. They are almost exactly at the same declination as Regulus so, using an equatorial mount, centre on Regulus, lock the declination axis and sweep towards the west 9 degrees. They are both close to 9th magnitude and may bee seen together with a telescope at low power or individually at higher powers. M65 is a type Sa spiral lying at a distance of 35 millin klight years and M66, considerably bigger than M65, is of type Sb. Type Sa spirals have large nuclei and very tightly wound spiral arms whilst as one moves through type Sb to Sc, the nucleus becomes smaller and the arms more open.
The second pair of galaxies, M95 and M96, lie a further 7 degrees to the west between the stars Upsilon and Iota Leonis. M95 is a barred spiral of type SBb. It lies at a distance of 38 million light years and is magnitude 9.7. M96, a type Sa galaxy, is slightly further away at 41 million light years, but a little brighter with a magnitude of 9.2. Both are members of the Leo I group of galaxies and are visible together with a telescope at low power.
There is a further ~9th magnitude galaxy in Leo which, surprisingly, is in neither the Messier or Caldwell catalogues. It lies a little below lambda Leonis and was discovered by William Herschel. No 2903 in the New General Catalogue, it is a beautiful type Sb galaxy which is seen at somewhat of an oblique angle. It lies at a distance of 20.5 million light years.
The constellation Virgo
Virgo, rising in the east in late evening this month, is not one of the most prominent constellations, containing only one bright star, Spica, but is one of the largest and is very rewarding for those with "rich field" telescopes capable of seeing the many galaxies that lie within its boundaries. Spica is, in fact, an exceedingly close double star with the two B type stars orbiting each other every 4 days. Their total luminosity is 2000 times that of our Sun. In the upper right hand quadrant of Virgo lies the centre of the Virgo Cluster of galaxies. There are 13 galaxies in the Messier catalogue in this region, all of which can be seen with a small telescope. The brightest is the giant elliptical galaxy, M87, with a jet extending from its centre where there is almost certainly a massive black hole into which dust and gas are falling. This releases great amounts of energy which powers particles to reach speeds close to the speed of light forming the jet we see. M87 is also called VIRGO A as it is a very strong radio source.
Below Porrima and to the right of Spica lies M104, an 8th magnitude spiral galaxy about 30 million light years away from us. Its spiral arms are edge on to us so in a small telescope it appears as an elliptical galaxy. It is also known as the Sombrero Galaxy as it looks like a wide brimmed hat in long exposure photographs.
The constellation Ursa Major
The stars of the Plough, shown linked by the thicker lines in the chart above, form one of the most recognised star patterns in the sky. Also called the Big Dipper, after the soup ladles used by farmer's wives in America to serve soup to the farm workers at lunchtime, it forms part of the Great Bear constellation - not quite so easy to make out! The stars Merak and Dubhe form the pointers which will lead you to the Pole Star, and hence find North. The stars Alcor and Mizar form a naked eye double which repays observation in a small telescope as Mizar is then shown to be an easily resolved double star. A fainter reddish star forms a triangle with Alcor and Mizar.
Ursa Major contains many interesting "deep sky" objects. The brightest, listed in Messier's Catalogue, are shown on the chart, but there are many fainter galaxies in the region too. In the upper right of the constellation are a pair of interacting galaxies M81 and M82 shown in the image below. M82 is undergoing a major burst of star formation and hence called a "starburst galaxy". They can be seen together using a low power eyepiece on a small telescope.
Another, and very beautiful, galaxy is M101 which looks rather like a pinwheel firework, hence its other name the Pinwheel Galaxy. It was discovered in1781 and was a late entry to Messier's calalogue of nebulous objects. It is a type Sc spiral galaxy seen face on which is at a distance of about 24 million light years. Type Sc galaxies have a relativly small nucleus and open spiral arms. With an overall diameter of 170,000 light it is one of the largest spirals known (the Milky Way has a diameter of ~ 130,000 light years).
Though just outside the constellation boundary, M51 lies close to Alkaid, the leftmost star of the Plough. Also called the Whirlpool Galaxy it is being deformed by the passage of the smaller galaxy on the left. This is now gravitationally captured by M51 and the two will eventually merge. M51 lies at a distance of about 37 million light years and was the first galaxy in which spiral arms were seen. It was discovered by Charles Messier in 1773 and the spiral structure was observed by Lord Rosse in 1845 using the 72" reflector at Birr Castle in Ireland - for many years the largest telescope in the world.
Lying close to Merak is the planetary nebula M97 which is usually called the Owl Nebula due to its resemblance to an owl's face with two large eyes. It was first called this by Lord Rosse who drew it in 1848 - as shown in the image below right. Planetary nebulae ar the remnants of stars similar in size to our Sun. When all possible nuclear fusion processes are complete, the central core collpses down into a "white dwarf" star and the the outer parts of the star are blown off to form the surrounding nebula.